Apparatus for making filters

ABSTRACT

Improved tobacco smoke filters, particularly cigarette filters, are prepared from a web of synthetic polymeric fibers having applied to at least one surface thereof a film-forming derivative of cellulose. Continuous processes and apparatus for the production of the web and filter are also described.

iie States Levers et a1.

[ Dec. 3, 1974 APPARATUS FOR MAKING FILTERS Inventors: William E.Levers; Charles 11. Keith, both of Charlotte, NC.

Assignee: Celanese Corporation, New York,

Filed: Mar. 24, 1972 Appl. No.: 237,904

Related us. Application Data Division of Ser. No. 36,746, May 13, 1970,

abandoned.

U.S. c1... 425/66, 28/1 CF, 19/65 T, 19/66 T, 156/167, 425/102, 425/363,425/289 1m. (:1. B29C 17/02 Field of Search 425/66, 92, 102, 105, 106,425/109, 4, 223, 224, 392, 371, 373, 363; 156/166, 167; 28/1 CF; 19/65T, 66 T References Cited UNITED STATES PATENTS Ouoss 425/106 X 3,017,309l/1962 Crawford et a1 156/161 3,025,563 3/1962 Carman et a1. 425/663,095,343 6/1963 Berger 28/1 CF 3,095,632 7/1963 Smith 19/65 T X3,144,025 8/1964 Erlich 19/66 T UX 3,148,101 9/1964 Allman, Jr. et a1.425/66 X 3,173,188 3/1965 Wexler 28/1 CF 3,323,961 6/1967 Gallagher 28/1CF 3,466,358 9/1969 Muller 425/66 X 3,522,342 7/1970 Nungesser et a1.425/66 X Primary ExaminerRobert L. Spicer, Jr. Attorney, Agent, orFirmPame1a D. Kasa [5 7 ABSTRACT Improved tobacco smoke filters,particularly cigarette filters, are prepared from a web of syntheticpolymeric fibers having applied to at least one surface thereof afilm-forming derivative of cellulose. Continuous processes and apparatusfor'the production of the web and filter are also described.

7 Claims, 3 Drawing Figures APPARATUS FOR MAKING FILTERS This is adivision, of application Ser. No. 36,746, now abandoned.

BACKGROUND OF THE INVENTION An acceptable tobacco smoke filter,particularly a cigarette filter, must exhibit a high degree offiltration of tobacco smoke particles, i.e., have high smoke removalefficiency, at an acceptable draw resistance, i.e., pressure drop. Thefilter must also be capable of economical continuous production.Furthermore, it must be of a firmness sufficient to avoid collapseduring smoking and must not unduly distort the taste and odor of thetobacco smoke.

Many materials including cellulose fibers and a variety of syntheticfibers have been suggested for use in tobacco smoke filters. Of thesematerials, only continuous filament cellulose acetate tow, and to alesser degree, paper, have met with any degree of commercial acceptance.

There is a continuing search for new tobacco smoke filters meeting theabove criteria and having improved smoke removal efficiencies.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide improved tobacco smoke filters exhibiting a high degree of smokeremoval efficiency with acceptable taste, firmness, draw resistance andeconomics.

It is another object to provide improved intermediate products useful inthe formation of filters having the above characteristics.

Other objects of the present invention reside in the provisions forapparatus and processes for manufacture of the aforesaid filters andintermediate products.

Still other objects, if not specifically set forth herein, will beobvious to the skilled artisan upon reading the detailed description ofthe invention with reference to the drawings.

DRAWINGS FIG. 1 is a perspective view of an apparatus suitable for thepractice of the present invention.

FIG. 2 is a side view of an apparatus suitable for use in forming theintermediate product.

FIG. 3 is a side view of an apparatus suitable for use in formingtobacco smoke filters from the intermediate product.

DETAILED DESCRIPTION OF THE-INVENTION Generally, the filters of thepresent invention are comprised of a condensed web of small diametersynthetic thermoplastic filaments, preferably of noncellulosiccomposition, which are bound together by a film-forming derivative ofcellulose.

Briefly, the intermediate products used in the preparation of theaforesaid filters are prepared by coating the fibers on at least onesurface of a web of synthetic organic thermoplastic fibers andpreferably substantially uniformly impregnating the web, with a solutionor dope of a filmforrning organic derivative of cellulose, removingsolvent from the dope to at least partially produce a film, flexing theweb to fracture or substantially destroy the film and produce amultiplicity of particles of the organic derivative of cellulose adheredto the fibers, applying a plasticizer to the web to render the particlestacky and condensing the web into filter form while the particles are ina tacky state.

Fibrous webs finding utility in the present invention may be preparedfrom a variety of synthetic, organic fibers including polyolefin,polyester, polyamide, and cellulosic fibers. The fibers in the web maybe in the form of a tow of continuous filaments, a staple roving orrandomly arranged as in a non-woven web.

Preferably, the web to be coated will have a total denier of from about25,000 to about 120,000, and preferably from about 45,000 to about65,000; a width of from about 2 to about 24 inches, and, for shippingpurposes, preferably from 2 to'about 8 inches; and a thickness fromabout 0.02 to about 0.25 inches.

The individual fibers comprising the web will ordinarily have a denierper filament of from about 0.0l to about 16 (equal to about l-45 micronsin diameter) with the lower denier per filament fibers, e.g., from about0.01 to about 1.0 (equal to about l-l2 microns in diameter) beingpreferred.

If a tow of continuous filaments is employed, the tow will ordinarilyhave a total denier of from about 45,000 to 120,000 and be comprised ofcrimped continuous filaments having up to about 40, and preferably fromabout 5 to about 15 crimps per inch and a dpf of from about 0.5 to about16. Such tows may be conveniently prepared, for example, from celluloseacetate or polyolefin filaments.

The preferred fibrous web for use in the present invention is a sprayspun web having a surface area'of from about 0.1 to about 2.0 M' lgm,and preferably, from about 0.4 to about 1.5 M /gm, comprised of arandomly arranged reticulatemass of fibers composed of a non-cellulosicpolymer, preferably a polyolefin such as polypropylene or polyethylene.Ideally, the fibers are composed of a polyolefin having an intrinsicviscosity of from about 0.4 to about 1.25, and preferably, from about0.6 to 0.75.

The dope applied to the web'is comprised of a solution of a film-formingorganic derivative of cellulose in a suitable solvent. Particularlydesirable film-forming materials are the celulose esters and celluloseethers, including, but not limited to, cellulose acetate, cellulosepropionate, cellulose acetate butyrate, cellulose acetate propionate,ethyl cellulose, methyl cellulose, sodium carboxymethyl cellulose,carboxymethyl hydroxyethyl cellulose, and mixtures thereof. Celluloseacetate, because of its cost and previous commercial acceptance isparticularly suitable.

The solvent employed in the preparation of the dope is not critical andwill vary somewhat depending on the film-forming compound employed.0rganic solvents such as acetone, methyl ethyl ketone, or methylenechloride, normally liquid organic ethers and esters are ordinarilysuitable. Water may also be used as a solvent bale may be used, anddirected to dope applicator 14 where dope 16 is applied to at least onesurface of the web.

In the drawing, dope applicator 14 is shown as a transfer roll device.It is to be understood, however, that other types of applicators may beemployed. For example, the cellulose acetate dope can also be readilyapplied with wick applicators, spray devices, and the like.

After web is coated on at least one surface with dope 16, and preferablysubstantially, uniformly impregnated, it is passed to a dryer 18 wherethe solvent is removed and the web is dried. Ordinarily, dryer 18 willbe comprised of a suitably heated chamber with a vacuum source whichdirects evaporated solvent to a recovery systen, not shown. Thestructure of the particular device is not critical, however, so long asthe web is substantially freed of solvent.

After solvent removal, treated web 10 may be taken up on a suitablecollection means 20, which may be a roll or bale, for subsequentprocessing or shipment, or the web may be directly processed intotobacco smoke filter rods.

The intermediate product or treated web 10, will be comprised of fromabout 10 to about 40 and preferably from about 20 to about 30 percent ofthe film-forming cellulosic derivative, the derivative forming afilm-like coating around and between at least a portion of the fibers.During collection for storage, the dried film may become somewhatfractured and discontinuous. This fracturing is not detrimental to theproperties of the web, however, for reasons which will become apparent.

In the preparation of filter rods, the web is directed from collector20, or drier 18, to flexing device 22 which further fractures orpartially destroys the continuous structure of the film and increasesthe flexibility of the web, and a multiplicity of particles of thecellulosic derivative adhered to the fibers.

As earlier noted, the intermediate product of the present invention isdesirably from about 2 to about 8 inches in width to facilitatepackaging and shipping. If webs of this width are employed, it isdesirable at this stage to transversely stretch the web to a width offrom 8 to 24 inches, in order to obtain the optimum filtrationproperties upon condensation of the web into a tobacco smoke filter.While this transverse stretching or opening can also occur afterplasticizing of the web, prior stretching is preferred in order toobtain optimum plasticizer distribution.

F lexing device 22 as illustrated in the drawing is comprised of aplurality of roll pairs at least one roll of each pair beingcircumferentially grooved. A flexing device of this type is particularlysuitable in the present invention in that it causes both flexing andstretching of the web to the desired width. This particular device doesnot constitute part of the present invention except as beingillustrative of the fact that flexing and transverse stretching of theweb can occur simultaneously.

Significant improvements in filtration properties are observed if, afterflexing and optional transverse stretching, web 10 is passed through thenip of a pair of patterning rolls 24. In the drawing, patterning rolls24 form part of flexing device 22. It is to be understood, however, thatin the general aspects of the invention, patterning rolls 24 may be adevice separate from flexing device 22.

Essentially, patterning rolls 24, at least one roll of the roll pairhaving a patterned surface, are adapted to afford a plurality ofpermanently depressed areas in the substrate. Said rolls 24 arepositioned substantially transverse to the tow path and are arrangedwith parallel axes. Ordinarily, one roll of the pair will be adjacentthe upper surface of the tow path, while the second roll will be mountedopposite said roll and below the tow path. However, the web may alsofollow a vertical path with a patterned roll mounted of either side ofsuch path. The rolls 24 may be mounted yieldably in contact or slightlyseparated. The rolls should be of a proximity,

however, sufficient to cause at least some permanent depression of thetow as it passes therebetween. Preferably, the separation of the rollsis from 0 to about 0.02 inches, and even more desirably from 0 to about0.01 inches. The separation, of course, will depend upon a thickness ofthe tow as determined by the total denier and width thereof. Websprocessed through rolls of the above separation will have an overallthickness of from about 0.1 to about 2.5 mm.

In order to obtain the advantages of the present invention, a variety ofpatterns may be imparted to the surface of the web material. Suchpatterns may comprise continuous depressed areas and/or continuouslands. For example, a waffle or quilted surface as illustrated in FIG. 2may be imparted to the surface of the web. In this pattern, either thecontinuous or discontinuous area may be compressed. The waffle orquilted pattern may also be oriented so that the edges of the patternare at an angle to the longitudinal axis of the web, in effect impartinga diamond-shaped pattern as shown in FIG. 3 to the surface of the web.Generally, it has been found that the preferred patterns of the presentinvention from the standpoint of the greatest relative reduction inpressure drop comprise grooves defining a path substantially parallel tothe longitudinal axis of the web. These longitudinal grooves preferablyform a straight line along the web, i.e., accordian pleats; sinusoidalor zig-zag grooves are also possible, however.

Desirably, the preferred rolls employed in the present inventionarecircumferentially or helically grooved, and will have from about 5 toabout and preferably from about 20 to about 45 grooves per inch. Thelands of the rolls will ordinarily be of about 0.03 to about 0.005 inchand more preferably from about 0.015 to about 0.008 inch in width. Thegrooves will ordinarily be about 0.035 to about 0.005 and preferablyfrom about 0.002 to about 0.001 inch in depth. The lands of a given rollwill ordinarily, but not necessarily, be of uniform width. In fact,lands which progressively decrease in width outwardly from the center ofthe patterned area may aid in the construction of a more uniform filter.Similarly, the depths of the grooves may be of difierential dimensionsacross the web.

Rod firmness can be improved by using rectangular or substantiallyrectangular grooves, since such grooves tend to yield a material which,upon gathering into rod form, has self-supporting, triangular-shaped,difficultly compressible channels. The term substantially rectangulargrooves is intended to define a groove wherein the angle from thevertical of the wall is from 0 to 45 and preferably from 0 to 30. It is,of course, within the scope of the present invention to use othergrooved shapes, e.g., semi-circular, trapezoidal, or triangular grooves.

In some instances, the use of heated patterned rolls has been found tobe of value in obtaining improved corrugation. When used, the heatedrolls will generally have a temperature of from about 25 to 225C andpreferably from about 110 to about l60 C.

Preferably, patterning rolls 24 are at least 2 inches in diameter, andmore preferably, from about 4 to about 8 inches in diameter. The widthof the patterned portion of the rolls will, of course, be determined, tosome extent, by the width of the web being structured. Generally, atotal patterning width of from about 8 to about 16 inches is sufficientfor most operations.

After flexing and optional transverse stretching and- /or patterning,web is directed to plasticizer applicator 26 where a plasticizer, i.e.,a solvation agent, is applied to the web to cause the cellulosicparticles to become tacky. In the drawing, plasticizer applicator 26 isa cylindrical plasticizer applicator of the type described in US. Pat.No. 3,387,992, issued June ll, 1968. Essentially applicator 26, iscomprised of a housing, a rotatable disc located within the housingbelow the path of the web and substantially transverse thereto, meansfor conveying a plasticizer to the rotatable disc and means forrecycling unused plasticizer. Other applicators which are adapted toapply plasticizer to a continuous fibrous web may also be used for thispurpose.

For example, applicators utilizing wicks or spray nozzles are alsousable.

Ordinarily, from about 3 to about percent plasticizer based on theamount of cellulosic derivative will be applied, with about 6 to about15 percent being preferable. Triacetin will normally be employed afterplasticizing, particularly when the cellulosic derivative is celluloseacetate. However, other organic solvents such as triethyl citrate,dimethyl ethyl phthalate, or the dimethyl ethers of triethylene ortetraethylene glycol may also be used. Water will also find utility as aplasticizer with certain of the hereinbefore described cellulosicderivatives.

The web, after being treated with a plasticizer, is directed into filterrod maker 28 where the web is condensed into tobacco smoke filter rodswhich will ordinarily be of about 8 mm in diameter and severed to 60 to180 mm in length. Filter rods of this length are desirable in that theyare readily severable into 6 filters of 10 to 30 mm in length forattachment to tobacco columns.

The following examples are presented for the purpose of illustrationonly and are not to be taken as in limitation of the present invention.

EXAMPLES 'l-6 Spray spun webs of polypropylene'fibers weresubstantially, uniformly impregnated with a dope of cellulose acetatepolymer dissolved in acetone. The coated webs were then dried and flexedto destroy the film-like properties of the cellulose acetate filmproduced. A triacetin plasticizer was applied to the webs which werethen patterned with 20 parallel, longitudinal, rectangular grooves perinch. The web was then condensed into cigarette filters of 20 mm inlength and 24.8 mm in circumference. The composition, based on totalweight of product, and surface area of the webs were as follows:

The pressure drops of filaments prepared from the above intermediateproduct was determined. The filaments were then attached to 65 mmtobacco columns and smoke nicotine and tar (total particulate matter,less nicotine and water) removal efficiencies were determined. Thefollowing results were obtained.

TABLE ll SMOKING PERFORMANCE Intermediate AP 84 & & & Com.

Product mm,H O SRE NRE TRE pressibility l 64 66.5 61.0 62.l 31.6 2 6259.3 53.2 53.7 NOT TESTED 3 65 53.7 48.6 48.0 NOT TESTED 4 60 59.6 55.654.4 38.2 5 55 56.3 50.6 48.3 43.8 6 67.3 64.0 62.4 3L6 For purposes ofcomparison, conventional cellulose acetate filters having a pressuredrop of from 55 to 70 mm water have a smoke removal efficiency of about42 to about 52 percent, a nicotine removal efficiency of about 32 toabout 42 percent, and a tar removal efficiency from. about 35 to about45 percent.

EXAMPLE 7 A band of crimped, continuous polypropylene filaments havingapproximately 20 crimps per inch, a denier per filament of 0.9 and atotal denier of 50,500 was substantially uniformly impregnated with adope of 6 percent, based on the weight of dope, of cellulose acetatepolymer dissolved in acetone, and dried to produce an intermediateproduct comprised of approximately 60 percent polypropylene fiber and 40percent cellulose acetate. This material was flexed and patterned with20 rectangular, longitudinal, parallel grooves per inch. Ten percenttriacetin based on the cellulose acetate was applied thereto. Theplasticized material was then formed into cigarette filters exhibitingdesirable smoke removal efficiencies, pressure drop, and firmness.

While the foregoing description has dealt only with the preparation of afilter from an impregnated web of a fibrous material, it is alsopossible to prepare satisfactory and often improved filters byincorporation of one or more other filtration materials into the webmaterial prior to' corrugation. Such materials include carbon, silicagel or other high surface area absorbents, granular polyurethanes,cellulose acetate flake, wood pulp, flock, liquid additives and othergas adsorbents or selective absorbents. Generally, up to about 20percent of these materials based on the weight of the filter may beemployed, with from about 5 percent to about 10 percent being preferablyutilized. Obviously, a multiplicity of, and tows comprising the same ofdifferent filamentary materials could be combined to form suitablefilter structures as described herein.

Filters prepared by the above method may be used as the sole filtrationmeans on a cigarette. It is, of course, possible to use filters preparedby the present invention as part of a dual or segmented filter. In thiscontext, the present filters are particularly suitable in combinationwith paper filters and conventional cellulose acetate filters.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit and scope of the invention.

What is claimed is: i

1. An apparatus for preparing improved cigarette filters comprising asupply means for providing a web of synthetic thermoplastic organicfibers having at least one surface thereof impregnated with afilm-forming derivative of cellulose which renders the web stiff,flexing and fracturing means for receiving, flexing and fracturing saidfilm-forming derivative of cellulose on said web, patterning means forembossing said web, plasticizing means for applying a plasticizer to atleast one surface of the flexed and embossed web, which plasticizermeans softens the fractured web and means for converting the plasticizedweb into a substantially cylindrical tobacco smoke filter rod.

2. The apparatus of claim 1 additionally comprising stretching meanspositioned after said flexing means for transversely stretching saidweb.

3. The apparatus of claim 1 additionally comprising patterning meansafter said flexing means for impressing a patterned configuration intoat least one surface of said web, said patterning means comprising apair of circumferentially or helically grooved rolls having 5 to groovesper inch, said grooves being from about 0.035 to 0.005 inch in depth.

4. The apparatus of claim 1 wherein said flexing means comprises aplurality of roll pairs at least one roll of each pair beingcircumferentially grooved.

5. The apparatus of claim 1 additionally including liquid applicatormeans for applying a film-forming derivative of cellulose in liquid formto said web and drying means for drying said applied cellulose.

6. The apparatus of claim 1 wherein the patterning means are heatedrolls.

7. The apparatus of claim 3 wherein said grooved rolls havesubstantially rectangular grooves, wherein the angle from the verticalof the groove walls is 0 to 30.

1. An apparatus for preparing improved cigarette filters comprising asupply means for providing a web of synthetic thermoplastic organicfibers having at least one surface thereof impregnated with afilm-forming derivative of cellulose which renders the web stiff,flexing and fracturing means for receiving, flexing and fracturing saidfilm-forming derivative of cellulose on said web, patterning means forembossing said web, plasticizing means for applying a plasticizer to atleast one surface of the flexed and embossed web, which plasticizermeans softens the fractured web and means for converting the plasticizedweb into a substantially cylindrical tobacco smoke filter rod.
 2. Theapparatus of claim 1 additionally comprising stretching means positionedafter said flexing means for transversely stretching said web.
 3. Theapparatus of claim 1 additionally comprising patterning means after saidflexing means for impressing a patterned configuration into at least onesurface of said web, said patterning means comprising a pair ofcircumferentially or helically grooved rolls having 5 to 80 grooves perinch, said grooves being from about 0.035 to 0.005 inch in depth.
 4. Theapparatus of claim 1 wherein said flexing means comprises a plurality ofroll pairs at least one roll of each pair being circumferentiallygrooved.
 5. The apparatus of claim 1 additionally including liquidapplicator means for applying a film-forming derivative of cellulose inliquid form to said web and drying means for drying said appliedcellulose.
 6. The apparatus of claim 1 wherein the patterning means areheated rolls.
 7. The apparatus of claim 3 wherein said grooved rollshave substantially rectangular groovEs, wherein the angle from thevertical of the groove walls is 0* to 30*.